Spiral wound membrane have often been produced by winding a membrane leaf or leaves, a permeate transfer sheet, and a spacer sheet around a perforated central collection tube.
A great number of spiral wound membranes are known from literature for example EP 0347174, U.S. Pat. No. 4,735,717 and U.S. Pat. No. 3,966,616, which documents disclose spiral wound membrane cartridges having collection tubes around which permeate transfer leaves, membrane leaves and space leaves are wound. U.S. Pat. No. 4,476,022 discloses a serrated product tube having perforations. A hollow tubular collection member provided with a plurality of randomly dispersed slots or apertures on its outer circumference is disclosed by U.S. Pat. No. 341,870, and U.S. Pat. No. 4,021,351 discloses a permeate collection tube fabricated from a plurality of interlocking tubular segments.
The central collection tube is the core around which the other cartridge materials are wound, and permeate is transferred from the membrane leaves to the interior of the collection tube. The central collection tube has heretofore been fabricated from a continuous length of commercially produced plastic tubing in which the required number of passages are provided by drilling holes or milling slits through the tube wall. While the raw material is not very expensive, the labour required for drilling or milling the number of transfer holes needed is great and costly.
Thus, one object of the present invention is to produce a less costly design of the spiral wound membrane and lessen the time of fabrication. Another object of the present invention is to improve the design of the spiral wound membrane and thus increase its performance. A further object is to improve the performance of the spiral wound membrane in connection with materials having higher viscosity.
Another further object is to improve the performance of the spiral wound membrane at lower temperatures.
Another further object is to improve the winding of membrane leaves around the core central collection tube.